Variable resistor with clutch limbs lifting slider against housing guides

ABSTRACT

A variable resistor adjustable by operation of a lead screw, with a post or slider having opposed upstanding elongate internally serrated limbs devised to grip the lead screw at opposed regions above the lead screw axis and thereby tend to lift the post, the latter having laterally extending elongate wings whose upper surfaces are lifted into engagement with guiding surfaces on the resistor housing, and the slider carrying a snap-on demountable contact.

United States Patent 72] inventors Banning; Joseph R. De Rouen, Rialto, both of, Calif. (21] Appl. No. 880,672 [22] Filed Nov. 28, 1969 [45] Patented Aug. 3, 1971 [73] Assignee Bourns, Inc.

[54] VARIABLE RESISTOR WITH CLUTCH LIMBS LIFTING SLIDER AGAINST HOUSING GUID 7 Claims, 12 Drawing Figs.

(52] US. Cl. 338/180,

' 338/183,338/202 [51] Int. Cl. l-l0le 9/02 [50] Field oiSearch 338/118, 160,161,176,180,182,183,202

[561 References Cited UNflED STATES PATENTS 2,895,116 7/1959 Morrison 338/180 Henry F. Martin 2,958,062 10/1960 Barden 338/180 3,050,704 8/1962 Dickinson 338/161 X 3,371,305 2/1968 De Lons 338/183 X 3,412,362 11/1968 Woods 338/183 3,497,858 2/1970 Norris 338/183 X Primary Examiner-Lewis H. Myers Assistant Examiner-Gerald P. Tolin Attorney-Fritz B. Peterson VARIABLE RESISTOR WITH CLUTCH LIMBS LIFTING SLIDER AGAINST HOUSING GUIDES BRIEF SUMMARY OF THE INVENTION a. The Environment of the Invention Lead screw adjusted potentiometers or variable resistors are characterized by an elongate resistance element and an elongate resistance element and an elongate return conductor, both extending parallel to the axis of a lead screw and spaced therefrom along the interior of a long resistor housing. Hereto fore a variety of dimensional variations among parts comprised in the resistor could be more or less compensating, or could be cumulative to either produce excessive contact pressure, or in the opposite extreme, to provide insufficient contact pressure. In the former situation, wherein the contact is pressed too severely against the element on which it is slidable in operation, excessive contact and/or resistance element wear occurs, greatly shortening the useful lifetime of the resistor. In the other situation, the unduly light pressure between contact and element results in excessive contact resistance variation (CRV) and a high degree of electrical noise generation. Thus it is desirable that the number of component dimensions which enter into the determination of the distance separating the lower face of the contact carrier or slider and the active surface of the resistance element should be I minimized.

b. The Present Invention The present invention, by unique constructions of the resistor housing, the slider, and the contact'member or device carried by and forming a functional part of the slider unit or device, accomplishes minimization of the noted number of significant dimensions, and concurrently permits or effects a significant reduction in the cost of manufacturing the resistor. Those results are attained in part by shaping the resistor housing to provide first and second spaced sets of reference surfaces such as shelves or ledges or like accurately spaced-apart surfaces, and guiding the slider by means of one pair of such surfaces and positioning the resistance element by means of another pair of the surfaces. The slider is shaped to permit it to assume various positions transversely of the lead screw, and also is shaped and made so it cams or draws itself into a position wherein the cooperating surfaces accurately position the slider relative to the resistance element, irrespective of the position of the slider relative to the lead screw. Thus, at most, two dimensions can enter into relative positioning or spacing of the contact base or support from the resistance element; and since both of those dimensions are, by virtue of molded part constructions of the slider body and the resistor body, extremely constant and unvarying, meritorious improvement in uniformity of characteristics over a large number of variable resistors is attained. Further, due to the constructions of the slider body and the contact whereby the contact is merely pressed into position on the slider body without any physical alteration or heat deformation of either component, the contact tension or pressure is uniform from resistorv to resistor throughout an indefinitely large number of resistors of the same model and construction.

The body of the resistor housing is preferably formed as an integral one-piece molded open-bottom elongate boxlike member providing an interior chamber arranged to receive, inter alia, the threaded portion of a lead screw, the slider and contact, and a resistance element device. The latter is in this preferred embodiment an elongate flat thin sheet of rigid ceramic material which serves as a substrate on one face of which the resistance element proper and a return conductor are deposited or formed. The boxlike member is provided, along its elongate interior, with two sets of reference surfaces, one set of which in essence provides a pair of slideways or guideways along which the novel contact-carrying slider body is guided and moved by action of the lead screw, and the other set of which serves to position the element-carrying face of the resistance element device. The two sets of reference surfaces are mutually parallel, whereby the paths of the slider body and the contact are parallel to the axis and active or working surface of the resistance element. Those two sets of surfaces are uniformly the same distance apart in all of successively molded resistor housing bodies; and constancy of the distance separating the slider body and the resistance element is achieved throughout a large number of like resistors by virtue of the fact that the position of the slider relative to the element is not dictated by the lead screw nor the lid or cover of the housing but only by the two sets of surfaces. The slider is so formed that it acts like a gripping cam and so it exerts forces on the lead screw which cause it to be continually urged into contact with the first set of the noted surfaces. The surfaces of that set or pair are so spaced-apart and the coaction of other surfaces are such that the torque transmitted to the slider incident to lead screw rotation is prevented from rotating or rocking the slider, whereby the latter member is caused to move solely along a restricted rectilinear path. The path is restricted by interior end wall surfaces in the housing member, against either of which endwalls the slider may be driven by sufficient rotation of the lead screw. Further rotation or overdriving of the lead screw following arresting of travel of the slider by either housing end wall is prevented from damaging the potentiometer by so forming the lead screw gripping limbs of the slider that they may resiliently yield to the forces exerted thereon by the thread of the screw and spread sufficiently to permit slipping of the thread relative to the limbs. Following such slipping, the limbs resiliently return to normal position, in which they are effective to translate the slider in the opposite direction incident to rotation of the lead screw in the opposite direction. The assembling of the slider onto the lead screw is reduced to a simple procedure of pressing the slider against the lead screw (or vice versa) whereby the limbs of the slider spread and embrace the lead screw. The slot between the limbs is sufficiently deep to provide a clearance space between the slider base and the lead screw, whereby the slider can accommodate itself to the noted guide surfaces. The thread-gripping interior faces of the slider limbs are provided with transversely elongate ridges or partial threads which normally are accommodated in the groove of the lead screw thread but which ride over the ridge of the lead screw thread when forced slipping occurs following arrestment of the rectilinear motion of the slider at either end of its path. The extra depth of the slot between the limbs of the slider permits the slider to move transversely relative to the axis of the lead screw and into guiding contact with the noted housing ledges; and thus the position of the slider transversely of the lead screw axis is independent of the lead screw.

The preceding general description of the invention and the environment thereof indicates that it is a primary object of the invention to provide general improvements in lead screw adjusted variable resistors.

Another object of the invention is to provide a combination of a resistor housing, a resistance element, a lead screw, and a lead screw driven contact-carrying slider, which combination permits accurate attainment of desired very light contact-toelement force and pressure irrespective of lead screw dimensional variations and eccentricities, with concurrent attainment of reduction of costs of parts and resistor assembly.

Another object of the invention is to provide a one-piece contact-carrying slider for a lead screw adjusted resistor, which slider is self-positioning in any of a plurality of positions transversely of the lead screw axis, whereby the slider can cooperate with other resistor parts to preclude any rocking or tilting of the slider and torestrict motion of the slider to only rectilinear motion parallel to a resistance element of the resistor.

Another object of the invention is to provide a slider and cooperating contact device for a lead screw adjustedresistor, in which the contact device is easily installed and easily removed from the slider without physical alteration of either and is securely locked in operating position on the slider incident to normal use in such resistor.

Other objects and advantages of the invention are hereinafter set out or made evident in the appended claims and the following detailed description of a specific presently preferred illustrative and exemplary physical embodiment of the invention.

A preferred physical embodiment of the invention is depicted in the accompanying drawings forming a part of this specification.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial view of a lead screw adjusted variable resistor in the form of a potentiometer incorporating the invention, to no particular or selected scale;

FIG. 2 is a grossly enlarged face view of the potentiometer pictured in FIG. 1, with portions of components broken away to reveal details of construction;

FIG. 3 is a transverse sectional view of the potentiometer, the section being taken as indicated by indicators 3-3 in FIG. 2;

FIG. 4 is an end view of the body of the slider comprised in the potentiometer, with the contact device removed;

FIG. 5 is a longitudinal sectional view of the body of the slider depicted in FIG. 4, the section being taken as indicated by indicators 5-5 in FIG. 4;

FIG. 6 is a transverse sectional view of the slider body, taken as indicated at 6-6 in FIG. 5;

FIG. 7 is a bottom view of the slider body;

FIG. 8 is a view in elevation of the slider assembly including the slider body and the conductive contact member carried by the slider body, indicating the positions of the contact when free, and when stressed as in use in the potentiometer;

FIG. 9 is a bottom view of the assembly depicted in FIG. 8; and

FIGS.'I0,' 11, and 12 are top, side and bottom views, respectively, of the contact device shown in the assembly depicted in FIGS. 8 and 9.

DETAILED DESCRIPTION The exemplary potentiometer (FIG. I) embodying the invention comprises a housing which is formed of a boxlike body 22 that is preferably produced as a molded member of insulation, and a cover 24 that is preferably produced as an elongate thin wafer of tired ceramic material such as alumina.

The cover has affixed thereto, as by being fired thereon, a thin elongate film or striplike resistance element 26 and a thin filmlike return conductor or collector 28 (FIG. 3), both of which components are exposed at the interior of a closed chamber 30 formed when the cover is assembled to the body 22. The cover also has affixed thereto a set of wire or pin terminals 32, 34 and 36, which connect with the ends of the resistance element 26 and with the collector 28, respectively. The cover is secured within the body 22 by adhesive means such as a sealant potting compound 38 which retains the edge or margin of the interior active face of the cover against longitudinally elongate downwardly facing ledges such as 40 (FIG. 3) formed as inverted steps along at least the opposed longitudinally extending walls bounding cavity 30. The body 22is formed to provide bearings for a lead screw 42 of which the slotted head 42h protrudes from one end of the housing. The structure thus far described is or may be like that of known lead screw adjusted potentiometers, and hence need not be further described in detail except in respect of novel features included in the present invention.

As in operation of previously known lead screw adjusted potentiometers, rotation of the lead screw on its axis, as by driver means engaged in the slot of head 42h, is effective to rectilinearly translate a slider and contact means along respective paths which in the present invention are exactly parallel to element 26 in chamber 30, with consequent change of the value of electrical resistance exhibited between either of the end terminals 32 and 34 and the middle terminal 36. Heretofore, rotation of the lead screw produced torque forces on the slider, which forces tended to rock or rotate the slider to some extent, with the consequence that the slider could and would thereafter rock reversely under the influence of vibration and would change the potentiometer setting. Attempts or efforts to avoid such rocking and the resultant change of tension of the contact and of the setting, by closely confining the slider along one or more of its faces, have been only partly successful. The lack of success in the noted efforts is in part due to the fact that dimensions of components are seldom if ever exact, with positive and negative dimensional tolerances coming into play. Partly, also, the difficulty has been due to the inability of the slider to change position relative to the axis of the lead screw. Such lead screws are at times eccentric, and vary in diametral dimensions. Thus in some instances the connection of the slider to the lead screw was such that upward and downward transverse movement of the slider relative to the lead screw axis was prohibited, so that the slider was required to respond to lead screw eccentricities and misalignments and so that the surfaces provided on the slider for engagement with antirotation surfaces provided on the potentiometer housing could not come into effective contact, whereby such surfaces were ineffective to prevent slider rocking and/or up and down movements relative to the element. The slider of the present invention not only avoids entirely the noted difficulty by permitting transverse (up and down) movement of the slider relative to the lead screw, but is so constructed as to generate forces which insure effective contact between the antirotation surfaces of the slider and housing and thus preclude rocking and transverse movement relative to the element and concurrently is such that assembly of the slider onto the shaft is very easily and expeditiously accomplished. The construction is such that the slider is caused to travel in a truly rectilinear path parallel to the active surface of the resistance element and is precluded from other movement, whereby extremely coonstant contact force or pressure is assured.

As indicated in FIGS. 4, 5 and 6, the slider 50 is formed as a molded structure of tough resilient and preferably slippery material, such as a synthetic resin polymer. It comprises a blocklike slider base 50b formed with opposed upstanding elongate resilient limbs 50m and 50!: each having a series of thread-simulating serrations or partial threads, such as 50s, along the interior face and each limb integral along its lower extent with the blocklike base 501;. The base 50b is formed with first and second guide surfaces 50f and 50g (FIG. 4), which, as is indicated in FIG. 3, are devised to engage and slide along a respective one of downwardly facing complementary elongate inverted shelves or ledges 22m and 22n formed along the interior sidewalls of the housing body and arranged parallel to the surfaces 40 against which the cover 24 rests. The limbs 50m and SIM of the slider are angular in cross section, and are so formed and dimensioned as to provide a deep elongate groove or slot 50p therebetween and so spaced that when forced onto a lead crew the serrated portions embrace the threaded portion of the lead screw along lines or regions that are above a transverse plane through the axis of the lead screw, that is, they engage the lead screw only above its axis. Thus the upper portions of the resilient lead screw embracing limbs of the slider act as lifting cams, and exert downwardly and inwardly directed forces on the lead screw that are effective to lift the slider base upwardly toward the lead screw and cause the surfaces 50f and 50g on toward lead screw and cause the surfaces 50f and 50g on the slider base to seat firmly against respective ones of ledges 22m and 22:1. The elongate slot 50p between the slider limbs is more than deep enough to accommodate such engagementor seating, and is dimensioned to provide a clearance, as indicated at C in FIG. 3, between the base 50b of the slider and the lowermost surface of the lead screw. Thus the slider can move vertically relative to the lead screw to accommodate itself to the guiding surfaces 22m and 22n. Also, the limbs are thus such that they may, while embracing the lead screw, spread apart and approach each other and yield individually as well as collectively, to accommodate eccentricities and dimensional variations in lead screws without binding or tendency to rotate with the lead screw. As is made evident in FIGS. 3 and 4, the transverse distance between the free limbs of the slider as formed is less than the diameter of the lead screw, so that the limbs must be resiliently spread for entry of the lead screw therebetween; and the cam action of the serrated interior faces of the limbs on the upper surface or are of the lead screw caused by the urge or tendency of the limbs to close or return to free form is permitted to continue indefinitely by virtue of the clearance space at C (FIG. 3) between the slider base 50b and the lead screw.

As will be apparent to those skilled in the lead screw adjusted potentiometer art, the slider will be arrested at either extremity of its rectilinear traverse upon being driven against an end wall of the chamber 30 by continued rotation of the lead screw. Further rotation of the lead screw in the same directiomfollowing such arrestment, is permitted by virtue of the resilience of the limbs and of the material of the slider. The pseudo, or partial, threads 50s formed on the inner faces of the limbs comprises alternating ridges and interridge grooves, as indicated in FIGS. 5 and 6. As the lead screw is overdriven after slider arrestment, the convolutions of the ridge or land of the thread of the lead screw act like a series of cams on the ridges of the limbs, forcing the ridges and the limbs to spread outwardly and further stressing them. The spreading action is followed by stressinduced inward movement of the limbs toward one another as the ridges of the limbs are passed by the land of the thread. The alternating outward spreading and inward approaching or closing actions of the limbs of the slider continue, without movement of the slider base and without any harmful effect on the mechanical structure or the electrical operation of the potentiometer, until overdriving of the leadscrew is terminated. Since at all times during the noted actions resulting from overdriving of the lead screw, the surfaces 50g and 50f of the slider are continually pressed upwardly into full contact with respective ones of ledges 22m and 22n; and thus the base 50b of the slider does not move nor vibrate, nor does the contact device attached thereto and presently to be described partake of any movement. Following any overdriving and slipping of the slider as described, rotation of the lead screw in the opposite direction results in immediate reengagement of the partial threads of the limbs with the thread of the lead screw, and reversal of translation of the slider and the contact device to effect adjustment of the resistance exhibited between selected terminals.

The slider is always permitted to bring and retain the noted surfaces 50g and 50f in firm contact with the ledges 22m and 22n, by virtue of the provision of the clearance space C (FIG. 3) at the lower extremity of the elongate slot or space between the limbs of the slider. In previous constructions, the curved surface at the bottom of the slot, between the lower extremities of the limbs, was held in contact with the lead screw, and thus the lead screw was the component that governed the vertical positioning of the slider. Such positioning of the bottom wall of the slider slot against the lead screw was in instances effected by forces exerted by the compression or stressing of the spring formed by the contact device carried by theslider; and as a consequence the contact spring pressure or force bearing on the resistance element was not only not uniform among a plurality of otherwise similar resistors but, more importantly, was necessarily much greater than the most desirable value. The present invention, by utilizing the camming action of the upwardly converging upper portions of the opposed limbs 50m and 50m of the slider on the uppermost half of the lead screw surface to lift and hold the slider against ledges 22m and 22h, entirely relieves the contact device from any part of the function of positioning the slider, and permits the contact device to be made and fonned to provide only the desired very light contact pressure on the resistance element. In the disclosed structural arrangement, that pressure or force is extremely uniform among like resistors of any lot manufactured from like parts, because the compression of the contact spring is principally dependent upon the spacing of the active surface of the resistance element from ledges 22m and 22n.

That spacing is held extremely uniform among resistors of like construction by virtue of the uniformity of the distance between the ledges and surfaces 40 against which the cover 24 is held in the assembled resistor.

The slider 50 is specially configured to permit easy and extremely uniform attachment of the contact device without stressing of the latter as is the case when riveting or heat swaging of plastic retainer buttons or like procedures of attaching the contact to the slider body are practiced. Thus, as is indicated in detail in FIGS. 7, 8 and 9, the slider base 50b is formed to provide a T-shaped abutment 50r protruding downwardly (as shown in FIG. 8) from the lower face 50e of the base. Further there is provided a second downwardly extending protuberance 50w extending across the entire width of base 50b and which protuberance is notched as at 50x and I 50y (FIG. 7) to provide inwardly inclined surfaces 50p and 50q separated by a continuation of the generally planar lower face 50:: of the slider base and by the middle portion of the protuberance 50w. Thus two separated recesses such as 50r (FIG. 8) are provided, each having one of parallel longitudinal internal walls and each extending inwardly from a respective side face of the slider base. Each of the noted recesses is dimensioned and situated to receive in close engagement with an inner wall a respective one of first and second cars 60:: and 60y (FIG. 12) of a conductive spring contact device 60 that is shown in detail in FIGS. 10, 11 and 12.

The contact device cooperates with the described recesses and protuberances so as to be inherently self-attaching and to preclude accidental removal or shifting in position of the device when in operation in the resistor, despite being so formed, relative to the cooperating surfaces of the slider base, that is may be merely dropped or slid into place and may be removed from the base by being shaken out or by being permitted fall free from the slider. Thus, as shown in FIGS. 10 and 12, the contact device is formed from a flat sheet or resilient metal, as by stamping or punching operation or operations, to provide the noted opposed ears 60x and 60y separated by a notch 601, and an elongate slot 60s terminated by an end face N. At respective sides of the slot, the device comprises the plural-tined collector-brushing contact limb 60b and the pluraltined element-brushing limb 600', all formed by stamping. The noted sheet is bent along a bend line indicated at A, and the individual tines 60c and 60d of the two limbs are cupped or bent as indicated in FIG. 11 to provide a plurality of contact points on each limb. The contact device is thus adapted to be applied to the slider base by a simple manipulation comprising insertion of the cars into the recesses 50r with concurrent seating of theseat N at the end of slot 60s against the face Z (FIG. 7) of the T-shaped protuberance 50!, and the ends and sides of the ears butting against the walls of the recesses. The

latter manipulation is performed with the slider topside-down and either in position to be applied by simple pressing onto the lead screw, or in position on the lead screw, as the housing body 22 is disposed topside-down and with its large opening ready for seating of the cover. Thus with the contact device seated on the slider and the slider pressed onto the threaded middle part of the lead screw, downward insertion of the cover into the open housing body, with the resistive element 26 facing downwardly, brings the elements on the cover into contact with the respective sets of contacts and compression or stressing of the contact limbs into the operating position approximately indicated by the dashline position in FIG. 8. Lateral or longitudinal movement of the contact device relative to the slider is prevented by engagement of end face N of the contact with face Z of the slider, and engagement of the ends and inner edges of the ears of the contact device with the wall surfaces bounding the recesses such as 50r in the protuberance 50w, as indicated in FIG. 9. Thus by the shapes and arrangements of the contact device, slider and housing body, and by the materials used, the objects of the invention are attained.

As will be evident to those skilled in the art, a presently preferred exemplary embodiment of the invention has been fully illustrated and described, and modifications and changes within the true spirit and scope of the invention will occur to others in the light of the disclosure of the noted embodiment. Hence the scope of the invention is as defined bythe appended claims.

Weclaim: 1. A lead screw adjusted variable resistor comprising: first means, including housing means providing an elongate chamber and comprising a body member providing a set of elongate downwardly facing shelflike guide surfaces therein along opposite sidewalls of said chamber; second means, including a resistance element having an elongate surface exposed in said chamber and disposed parallel to said guide surfaces; third means, including an elongate lead screw, journaled in said housing means and having a threaded portion disposed in said chamber with the longitudinal axis thereof disposed substantially parallel to said element; and I fourth means, including a contact-carrying slider having a base presenting first and second bearing surfaces at opposite sides thereof arranged to slide along respective ones of said guide surfaces, said slider having opposed elongate upstanding resilient limbs separated by a lead screw receiving slot, said limbs resiliently embracing said lead screw only along areas above the lead screw axis and thereby exerting forces effective to lift said base portion toward said lead screw and said bearing surfaces into forceful contact with said guide surfaces, said slot being of such depth that said base is spaced from and out of contact with the lower half of the arcuate surface of said lead screw, said fourth means including a contact device translated with said slider incident to rotation of said lead screw, said contact device being stressed and brushing on said resistance element;

whereby said slider and said contact device are inhibited from rocking or other deviation from rectilinear path of movement incident to operation of said lead screw despite eccentricity or other undesirable shape or positioning of said lead screw relative to said element and the force exerted by said contact device on said resistance element is independent of the shape and diametral dimensions of said lead screw.

2. A variable resistor as defined in claim 1, in which said housing body member provides a second set of downwardly facing surfaces parallel to said shelflike guide surfaces, and in which said first means comprise a housing cover on a flat surface of which said resistance element is supported and which cover has said surface in contact with said second set of downwardly facing surfaces, whereby said resistance element is precisely positioned relative to the rectilinear path of movement of said slider to maintain unvarying stress in said contact device during traversal along the extent of said element.

3. A variable resistor as defined in claim 1, in which said slider base comprises means forming first and second longitudinally extending recesses at opposite sides thereof separated by a wall-forming portion providing opposed longitudinal walls and means providing a wall-forming abutment longitudinally spaced from said recesses and providing a wall extending transversely of said base, and in which said contact device comprises first and second ears seated in respective ones of said recesses and each abutting against respective ones of said longitudinal walls and further defining a slot with an end boundary wall against which the transverse wall of said abutment abuts, whereby said contact is detachably secured to said slider and held against lateral and longitudinal motion relative to said slider.

4. A variable resistor as defined in claim I, in which said body-housing member provides a second set of downwardly facing surfaces parallel to said shelflike guide surfaces, and in which said first means comprise a flat housing cover on a face of which said resistance element is supported and which cover is disposed with portions of said face in face-to-face contact with said second set of downwardly facing surfaces to precisely position said element parallel to the rectilinear. path of movement of said slider, and in which resistor said slider base comprises means forming first and second recesses at opposite sides thereof extending inwardly therein and bounded therein by respective sets of separated walls, said slider base comprising a transverse abutment forming a transverse wall, and in which resistor said contact device comprises first and second ears snugly seated in respective ones of said recesses in contact with said walls, said contact device having means forming a transverse face against which said transverse wall of said abutment presses, whereby said contact device in said resistor is restricted to movements strictly parallel with said resistance element during rotation of said lead screw and whereby force exerted by said contact device on said resistance element is as small as desired and is uniform during all operations of said resistor.

5. A lead screw adjusted variable resistor comprising: first means, including a housing means providing an elongate chamber and opposed elongate parallel guide surfaces therein; second means, including an elongate resistance element extending longitudinally of said chamber and having an active surface exposed in said chamber parallel to said guide surfaces, and terminal means for said element; third means, including an elongate lead screw journaled in said housing and having a threaded portion exposed in said chamber with a lower half of the periphery thereof facing toward said element and an upper half of the periphery facing away from said element; fourth means, including a slider having upstanding opposed resilient limbs and a base integral with said limbs, said slider being disposed in said chamber with said base between said element and said lead screw and out of contact with said lead screw, said limbs resiliently clasping and engaging said leadscrew along respective portions of said upper half of the periphery thereof and exerting downwardly and inwardly directed forces thereon tending to lift said base toward said lead screw and effective to bring said base into guiding engagement with said parallel guide surfaces whereby said base is constrained to rectilinear movements along said guide surfaces independently of the shape and dimensions and operation of said lead screw and whereby said slider is traversed along said guide surfaces incident to lead screw rotation; and fifth means including a resilient contact device carried by said slider, said contact device having a contact bnishing on said element. 6. A lead screw adjusted variable resistor as defined in claim 5, in which said base of said slider comprises means forming opposed separated recesses therein and an abutment providing a wall extending transverselyof said base, and in which said contact device comprises opposed spaced ears complementary to and snugly engaging said base in respective ones of said recesses and further comprises first and second contact limbs separated by a slot terminated by a wall complementary to and abutting against said wall of said abutment,

whereby said contact device is detachably secured in operative position on said slider and is thereon restrained against longitudinal and lateral movements thereon relative to said slider. 7. A lead screw adjusted variable resistor comprising: first means, including housing means providing an elongate chamber characterized by a pair of downwardly facing parallel shelflike guide surfaces along opposite sides of the chamber and a pair of downwardly facing ledges parallel to said guide surfaces; second means, including a lead screw journaled for rotation I in said housing and having a threaded portion exposed along a portion of the interior of said chamber; third means, including an elongate housing cover having thereon a resistance element, said cover positioned against said ledges and secured to said first means and and holding said base out of contact with said lead screw; and

fifth means, including a resilient contact device having ears and wall-forming means cooperating with respective complementary wall-forming means on said slider base to detachably secure said contact device to said base and to restrain said contact against any longitudinal and transverse movement relative to said base in said chamber, said contact device having a contact brushing on said active face of said element. 

1. A lead screw adjusted variable resistor comprising: first means, including housing means providing an elongate chamber and comprising a body member providing a set of elongate downwardly facing shelflike guide surfaces therein along opposite sidewalls of said chamber; second means, including a resistance element having an elongate surface exposed in said chamber and disposed parallel to said guide surfaces; third means, including an elongate lead screw, journaled in said housing means and having a threaded portion disposed in said chamber with the longitudinal axis thereof disposed substantially parallel to said element; anD fourth means, including a contact-carrying slider having a base presenting first and second bearing surfaces at opposite sides thereof arranged to slide along respective ones of said guide surfaces, said slider having opposed elongate upstanding resilient limbs separated by a lead screw receiving slot, said limbs resiliently embracing said lead screw only along areas above the lead screw axis and thereby exerting forces effective to lift said base portion toward said lead screw and said bearing surfaces into forceful contact with said guide surfaces, said slot being of such depth that said base is spaced from and out of contact with the lower half of the arcuate surface of said lead screw, said fourth means including a contact device translated with said slider incident to rotation of said lead screw, said contact device being stressed and brushing on said resistance element; whereby said slider and said contact device are inhibited from rocking or other deviation from rectilinear path of movement incident to operation of said lead screw despite eccentricity or other undesirable shape or positioning of said lead screw relative to said element and the force exerted by said contact device on said resistance element is independent of the shape and diametral dimensions of said lead screw.
 2. A variable resistor as defined in claim 1, in which said housing body member provides a second set of downwardly facing surfaces parallel to said shelflike guide surfaces, and in which said first means comprise a housing cover on a flat surface of which said resistance element is supported and which cover has said surface in contact with said second set of downwardly facing surfaces, whereby said resistance element is precisely positioned relative to the rectilinear path of movement of said slider to maintain unvarying stress in said contact device during traversal along the extent of said element.
 3. A variable resistor as defined in claim 1, in which said slider base comprises means forming first and second longitudinally extending recesses at opposite sides thereof separated by a wall-forming portion providing opposed longitudinal walls and means providing a wall-forming abutment longitudinally spaced from said recesses and providing a wall extending transversely of said base, and in which said contact device comprises first and second ears seated in respective ones of said recesses and each abutting against respective ones of said longitudinal walls and further defining a slot with an end boundary wall against which the transverse wall of said abutment abuts, whereby said contact is detachably secured to said slider and held against lateral and longitudinal motion relative to said slider.
 4. A variable resistor as defined in claim 1, in which said body-housing member provides a second set of downwardly facing surfaces parallel to said shelflike guide surfaces, and in which said first means comprise a flat housing cover on a face of which said resistance element is supported and which cover is disposed with portions of said face in face-to-face contact with said second set of downwardly facing surfaces to precisely position said element parallel to the rectilinear path of movement of said slider, and in which resistor said slider base comprises means forming first and second recesses at opposite sides thereof extending inwardly therein and bounded therein by respective sets of separated walls, said slider base comprising a transverse abutment forming a transverse wall, and in which resistor said contact device comprises first and second ears snugly seated in respective ones of said recesses in contact with said walls, said contact device having means forming a transverse face against which said transverse wall of said abutment presses, whereby said contact device in said resistor is restricted to movements strictly parallel with said resistance element during rotation of said lead screw and whereby force exerted by said contact device on said resistance element is as Small as desired and is uniform during all operations of said resistor.
 5. A lead screw adjusted variable resistor comprising: first means, including a housing means providing an elongate chamber and opposed elongate parallel guide surfaces therein; second means, including an elongate resistance element extending longitudinally of said chamber and having an active surface exposed in said chamber parallel to said guide surfaces, and terminal means for said element; third means, including an elongate lead screw journaled in said housing and having a threaded portion exposed in said chamber with a lower half of the periphery thereof facing toward said element and an upper half of the periphery facing away from said element; fourth means, including a slider having upstanding opposed resilient limbs and a base integral with said limbs, said slider being disposed in said chamber with said base between said element and said lead screw and out of contact with said lead screw, said limbs resiliently clasping and engaging said leadscrew along respective portions of said upper half of the periphery thereof and exerting downwardly and inwardly directed forces thereon tending to lift said base toward said lead screw and effective to bring said base into guiding engagement with said parallel guide surfaces whereby said base is constrained to rectilinear movements along said guide surfaces independently of the shape and dimensions and operation of said lead screw and whereby said slider is traversed along said guide surfaces incident to lead screw rotation; and fifth means including a resilient contact device carried by said slider, said contact device having a contact brushing on said element.
 6. A lead screw adjusted variable resistor as defined in claim 5, in which said base of said slider comprises means forming opposed separated recesses therein and an abutment providing a wall extending transversely of said base, and in which said contact device comprises opposed spaced ears complementary to and snugly engaging said base in respective ones of said recesses and further comprises first and second contact limbs separated by a slot terminated by a wall complementary to and abutting against said wall of said abutment, whereby said contact device is detachably secured in operative position on said slider and is thereon restrained against longitudinal and lateral movements thereon relative to said slider.
 7. A lead screw adjusted variable resistor comprising: first means, including housing means providing an elongate chamber characterized by a pair of downwardly facing parallel shelflike guide surfaces along opposite sides of the chamber and a pair of downwardly facing ledges parallel to said guide surfaces; second means, including a lead screw journaled for rotation in said housing and having a threaded portion exposed along a portion of the interior of said chamber; third means, including an elongate housing cover having thereon a resistance element, said cover positioned against said ledges and secured to said first means and disposed with an active face of said element exposed in said chamber parallel to said guide surfaces; fourth means, including a slider having resilient upstanding limbs thereof engaging said lead screw for traversal thereby along an extent of said chamber incident to rotation of said said lead screw, and said slider having a base with upwardly facing bearing surfaces bearing on said guide surfaces; said first means and said fourth means comprising means restricting said slider to rectilinear movements along a path parallel to said active face of said resistance element and holding said base out of contact with said lead screw; and fifth means, including a resilient contact device having ears and wall-forming means cooperating with respective complementary wall-forming means on said slider base to detachably secure said contact device to said base and to restrain said contact against any longitudinaL and transverse movement relative to said base in said chamber, said contact device having a contact brushing on said active face of said element. 